Semiconductor devices equipped with semiconductor light-emitting elements are widely known. One of these types of semiconductor devices, shown in FIG. 4, is made by mounting a semiconductor light-emitting element in a submount 3. FIG. 4 is a simplified cross-section drawing illustrating how the conventional semiconductor device is made. The conventional method for making the semiconductor device will be described, with references to FIG. 4.
As shown in FIG. 4, in the conventional method for making a semiconductor device 1, the submount 3 is prepared for mounting of a laser diode 2, which serves as the semiconductor light-emitting element. The submount is formed from: a ceramic substrate 4; a layered film (Ti/Pt film layer 5) formed on this substrate from a film containing titanium (Ti) and a film containing platinum (Pt); a gold (Au) film 6 formed on the layered film and serving as an electrode layer; a barrier layer 107 formed on this film containing platinum (Pt); and a solder layer 108 formed on this barrier layer containing gold (Au) and tin (Sn). The layered Ti/Pt film, the Au film, the solder barrier layer, and the solder layer can be formed using conventional film-forming methods such as vaporization, sputtering, or plating and conventional patterning methods such as photolithography or metal masking.
After preparing the submount as shown in FIG. 4, the solder on the submount is heated and melted and the laser diode serving as the semiconductor light-emitting element is mounted on a predetermined position on the solder (a die bond step is performed). Then, a heat sink not shown in the figure is connected and secured to the back of the submount using solder or the like, resulting in the semiconductor device equipped with the semiconductor light-emitting element.
In order to reduce thermal damage to the semiconductor light-emitting element during the semiconductor light-emitting element die-bonding step, the solder layer may be formed from solder that has a melting point lower than that of the AuSn-based solder described above, e.g., lead (Pb) tin (Sn) based solder or silver (Ag) tin (Sn) based solder. If an AuSn-based solder is used, a lead-free product can be provided.
There is currently a trend toward higher output in semiconductor light-emitting element to handle applications such as higher output in laser processing machines and higher write speeds in CD and DVD devices. The semiconductor devices used in these require higher degrees of practical reliability. One requirement for this is a high bonding strength between the semiconductor light-emitting element and the submount.